The main thing with a deer decoy, is to use it in an open area where the deer can see it in advance. 80 yards is good, but further is better. They don't like being surprised by walking upon a strange deer....because they're familiar with the deer in their area.
If you use a buck decoy, only use 1 antler. It shows less dominance and an approaching buck will feel less intimidated.
Face a buck decoy towards YOUR location, an approaching buck will want to face his opponent and this will put him in a good shot position.
Quite the opposite for doe decoys. Face them away from YOUR location, because an approaching buck will want to get behind her to check her scent to see if she's in heat and/or receptive. Does may or may not approach a doe decoy.
Girls are fickle. I've seen a doe walk up to my doe decoy, squat and pee next to it, all the while scraping the ground, in attempt to show her dominance. I've seen other does check the decoy from time to time, but kept their distance by 25 yards or more. Didn't spook, but didn't like the decoy either.
Personally, I've stopped using deer decoys. They're a pain to carry in and out of the area. Plus, most of them are noisy.
I have had good results using hen turkey decoys, for deer hunting. Deer trust turkeys, but turkeys don't trust anything.
I'm sitting on the ground, wearing a leafy suit, only 12 yards behind these does (downwind) and they never gave me a look.